This invention relates to an apparatus for molding a plurality of three-dimensional articles from a material capable of flowing and solidifying.
More particularly, this invention relates to a continuous linear apparatus for molding a plurality of three-dimensional articles which can be discrete or integrally attached to a base in a single operation without utilizing mold gates, runners, sprues, and avoiding shrinkage and sink marks in the molded articles.
Injection and extrusion techniques are widely used for molding melt-formable material such as thermoplastic resins and metals. In injection molding, for economic reasons, a plurality of articles are molded at the same time using a system of runners and gates for each of the individual mold cavities. The gates are normally very small openings to facilitate separation of the molded articles from the injection mold runner. This leaves voluminous sprues which results in wastage because they serve no useful purpose after molding and have to be reground for remolding. Recycle of previously molded material has disadvantages in the fact that polymers commonly undergo physical and chemical degradation upon molding and grinding. In addition, injection molding has been plagued by shrinkage of the molded parts which occurs as the molded parts cool in the mold. This results in off-tolerance articles which are generally characterized by varying dimensions and sink marks.
The present invention provides a unique molding system wherein sprues and runners are eliminated and mold shrinkage and consequent sink marks are minimized. The invention can be carried out without material residues which means that a plurality of three-dimensional articles can be consistently molded from virgin material. The present invention is also characterized by the fact that there is minimum breakdown of the molecular structure or other degradation of the material being molded, such as occurs due to lengthy heating, recycling, etc. The present invention is further characterized by an ability to mold a plurality of three-dimensional articles which can be discrete or integrally attached to a base and which can have a structure heretofore only obtainable using a sequence of specialized techniques. Extremely small articles having microscopic details can be molded in thick profusion.
The present invention, therefore, makes it possible to rapidly and efficiently mold a plurality of three-dimensional articles in a single step. Preferably the apparatus of the invention is operated continuously in an endless manner.